Rare metal asteroids could have exploded molten iron

The metal asteroid Psyche has mystified scientists because it is less dense than it should, given its iron-nickel composition. Now, a new theory could explain the low density and the metallic surface of Psyche.

Unlike most asteroids, Psyche seems to be composed mainly of iron and nickel instead of rocky rubble. Metal-rich asteroids are thought to have formed in the collision between primordial planetesimals, removing much of the outer material and leaving behind internal metal nuclei, which subsequently cooled and solidified from the outside towards l & # 39; inside. During this cooling process, an alloy of iron, nickel and lighter elements such as sulfur, melted, could have flowed to the surface through fluid-filled cracks, called dikes, covering a rocky layer at the top.

"We call these processes collectively" ferrovolcanism, "said Brandon C. Johnson, associate professor of Earth and Atmospheric Science at Purdue University.

The theory is detailed in a research article published in the journal Nature Astronomy Monday, September 16th. The paper was co-authored by Johnson; Michael M. Sori, associate researcher at the lunar and planetary laboratory of the University of Arizona; and Alexander J. Evans, Assistant Professor of Earth, Environmental and Planetary Science at Brown University.

Meteorites called pallasites are thought to be a mixture of base materials and mantle, possibly mixed by ferrovolcanism. The pockets of liquid metal, mixed with sulfur, are less dense than the surrounding solid materials, which produces an "overpressure" which can eventually cause the propagation of dykes and allow ferrovolcanism to occur.

Researchers have determined to what extent these dykes should spread to make volcanism possible.

"Our calculations suggest that ferrovolcanic eruptions may be possible for small metal-rich bodies, particularly for sulfur-rich melts and bodies with coats slimmer than about 35 kilometers or bodies where the mantle has been thinned. locally by large impact craters, "Johnson said. .

NASA's next space mission, Psyche, will help scientists test this theory. The ferrovolcanic eruptions could explain the low density of Psyche, which exists despite radar evidence and other scientific evidence of a metal surface composition. Psyche, the largest known metal asteroid in the solar system, is located in the asteroid belt between Mars and Jupiter. Its density is estimated at about half that of an iron meteorite.

The researchers hypothesized that the asteroid could consist of two layers, a metal core being surrounded by a lower density mantle made up of rocky materials.

"The ferrovolcanism may have transported the base material to the surface, causing radar detection of metal," Johnson said.

Research is ongoing, future work using more sophisticated modeling to study how ferrovolcanism could occur and possibly to study Psyche's evolution.

No spacecraft has yet visited a metallic asteroid and the concept of ferrovolcanism relies on mathematical models. NASA plans to launch the space probe in 2022. This mission could allow scientists to confirm the theory and answer questions about the role of metal asteroids in the evolution of the solar system.